The present invention concerns a circuit for controlling the power supply of a consumer, as well as a method of operating a circuit. The present invention especially concerns a low-interference power supply of a consumer with current pulses.
FIGS. 1-3 show a circuit as it is currently known. A known circuit 100 comprises a switch mode current source 1 SMC. The current source 1 is controlled by means of a control system 2, so that it is possible to maintain the power I1 supplied by the current source 1. Here the control system comprises a current measuring device via a resistor 3 in order to guarantee a respective control of the current source.
Furthermore, the circuit 100 comprises inductance 4, as well as a consumer 10 that is supplied with power by means of the current source. In an exemplary manner the consumer 10 is depicted as a diode operating in forward direction.
Parallel to the consumer 10, the circuit 11 comprises a first switch 7 which is controlled via a first driver unit 6. For this purpose, the first driver unit 6 is supplied with a pulse control signal 5 consisting of pulses and pulse intervals so that during the pulse interval the switch 7 is conductively controlled via a driver unit 6, and during a pulse the switch is suddenly block controlled.
The functionality of the known circuit is divided in three phases P1, P2 and P3, depending on the pulse control signal 5. FIGS. 1-3 provide a schematic picture of the three phases, whereas FIG. 1 shows the first phase, FIG. 2 the second phase, and FIG. 3 the third phase.
The pulse control signal consists of pulses and intermediate pulse intervals. In the present description the first pulse interval is denoted with P1, a subsequent pulse with P2, and a second pulse interval following pulse P2 is denoted with P3.
In the currently known circuit a second switch 13 has been provided which is connected in series to the consumer 10 and parallel to the first switch 7. This second switch 13 is actuated anti-phase to the first switch, which means that during the process of closing the first switch the second switch is opened and vice versa. In the context of the present invention, the term “closing” a switch means that the switch is conductively controlled by the respective driver unit. Similarly, the term “opening” a switch means that the switch is block controlled by the respective driver. Furthermore, a load 14 has been provided which is arranged in series to the consumer 10 and parallel to the first switch 6 and which comprises high load voltage. In this way it is possible to reduce considerably the fall time.
Subsequently, by means of FIGS. 1, 2 and 3, the functionality of the known circuit 100 is explained. FIG. 1 depicts the first phase P1 of the pulse control signal 5, FIG. 2 the second phase P2 of the pulse control signal 5, and FIG. 3 the third phase P3 of the pulse control signal 5.
FIG. 1 shows a pulse inverter 15 which inverts the pulse control signal 5 and transmits it to a second driver unit 12. In its functionality, the second driver unit 12 corresponds to the first driver unit 6 and is used to actuate the second switch 13. The load 14 is connected in parallel to the second switch 13.
FIG. 1 provides a schematic picture of the first phase P1 of the pulse control signal 5. During the pulse interval, the first switch 7 is conductively controlled and the second switch 13 is block controlled. The adjusted power I1, which has been impressed by the current source 1, flows through the inductance 4 and the first switch 7 back to the current source 1. The consumer 10, the load 14 and the second switch 13 are currentless.
FIG. 2 provides a schematic picture of the second phase P2, namely the pulse signal. By means of the pulse signal the first switch 7 is suddenly block controlled and, at the same time, the second switch 13 is conductively controlled so that the power I1 impressed via the current source 1 no longer flows through the first switch 7 but, because of the behavior of the current source 1 and inductance 4, said power flows back with a short rise time to the current source 1 in the form of pulses and square waves through the consumer 10 and the second switch 13.
FIG. 3 provides a schematic picture of the third phase P3, namely the pulse signal. Also in this pulse interval the first switch 7 is conductively controlled and, at the same time, the second switch 13 is block controlled. In this way the consumer 10 becomes currentless the same as the second switch 13 and the impressed power I1 and flows again back to the current source 1 via the inductance 4 and the first switch 7.
At the start of the third phase P3 power I2 flows through the consumer 10 because of the magnetic energy stored in the circuit inductances 8, 9 during the second phase P2. At the start of the third phase P3 the power I2 has the same value as power I1.
However, as time increases, the power is reduced until it reaches zero.
For this purpose, parallel to the second switch 13, a load 14 has been provided which can be a Zener diode with high Zener voltage. At the load 14 the decaying power I2 generates a load voltage UL which together with the secondary voltage UV of the consumer 10 forms an overall voltage with regard to the fall time t of the power I2. The load 14 is designed in such a way that it produces high load voltage UL, resulting in a very short fall time of the power I2.
If the secondary voltage UV and the load voltage UL are not power-dependent, the following applies to the fall time t of the power I2:
  t  =                    I        1            ⁡              (                              L            1                    +                      L            2                          )                            U        V            +              U        L            
For example, in case of a circuit inductance of respectively 50 nH, a load current of 100 A, a secondary voltage UV of 2V, and a load voltage UL of 100 V, the fall time results in:
  t  =                    100        ⁢                                  ⁢                  A          ·                      (                          50              +              50                        )                    ·                      10                          -              9                                      ⁢        H                              2          ⁢                                          ⁢          V                +                  100          ⁢                                          ⁢          V                      =                  98        ·                  10                      -            9                              ⁢      s      
Because of the anti-phase actuation of both switches the power I2 can be directed to zero via a load with high load voltage within a short period of time.
In a known circuit the switch mode current source in particular can cause high frequency interferences in the control unit. As shown in FIG. 4, the control system 2 can be coupled with the ground 19, i.e., with the housing and/or the earth, in order to reduce these high frequency interferences. The coupling with the ground can take place in galvanic or capacitive manner or at high frequency by means of a capacitor 18 so that the ground (Gnd) of the control system 2 is connected with a metallic housing which, in turn, is electrically connected with earth 19.
FIG. 4 shows that, besides the circuit inductances 8, 9, the known circuit comprises a first line capacity 16 and a second line capacity 17 to the earth, which line capacities are shown in the equivalent circuit diagram in FIG. 4 as capacitors 16, 17.
By means of the circuit shown in FIG. 4, it is possible to minimize the high frequency interferences. However, the circuit shows several disadvantages. The known circuit has especially the disadvantage that in the various phases of the pulse control signal 5 power flows through the ground 19, i.e., through the housing or the earth. Subsequently, by means of FIGS. 4-8, this is explained in more detail.
FIG. 4 shows the first phase P1, which is the pulse interval. During the first phase P1, the first switch 7 is conductively controlled, whereas the second switch 13 is block controlled. The adjusted power I1, which has been impressed by the current source 1, flows through the inductance 4 and the first switch 7 in the line between D and C back to the current source 1.
FIG. 5 shows the time period between the end of phase P1 and the start of the second phase P2 of the pulse control signal 5. At this the first switch 7 is suddenly block controlled and, at the same time, the second switch 13 is conductively controlled. The voltage at the first switch 7 jumps to very high values, for example, several 100 V, because the current source 1 and especially the inductance 4 make an attempt to maintain the current flow I1. However, at first, both circuit inductances 8, 9 prevent a current flow through the consumer 10. Therefore, the current now flows suddenly via the first line capacity 16, through the metallic housing 19 or through the earth 19 and via the capacitor 18 back to the current source 1.
In this phase considerable high frequency interferences occur and, at the same time, a high frequency interference voltage occurs in the line between D and C, because this line is suddenly supplied with power.
A further disadvantage is the fact that, at the moment of the voltage jump at the first switch 7, the potential at point A in reference to earth jumps to a positive value corresponding to the voltage at the first switch 7. On the other hand, because of the galvanic or high frequency grounding of the control system 2, the potential at point B remains completely or nearly at earth potential. In case the circuit inductances 8, 9 values are equal, the potential at the consumer 10 in reference to earth jumps to half the value of the potential at point A.
If the consumer 10 is not adequately insulated to ground 19, it can result in a breakdown or destruction of the consumer 10.
FIG. 6 shows the second phase P2. In this phase further high frequency interferences can occur if, as shown in FIG. 6, the consumer 10 has assumed the power I1, because now there suddenly no power flows any longer via the first line capacity 16, through the metallic housing or through the earth 19 and via the capacitor 18 and, at the same time, the line between D and C is suddenly supplied again with the power I1.
FIG. 7 shows the time period between the end of the second phase P2 and the start of the third phase P3 of the pulse control signal 5. Here, the first switch 7 is suddenly conductively controlled and, at the same time, the second switch 13 is block controlled. The power I1 now flows again via the first switch 7 back to the current source 1. At the same time, because of the energy stored in the circuit inductances 8, 9, an impressed power I2 continues to flow through the consumer 10. Since the second switch 13 is blocking, power I2 flows (as shown in FIG. 7) suddenly back in the line between C and D, via the second line capacity 17, through the metallic housing or through the earth 19 and via the capacitor 18.
At this considerably high frequency interferences occur and, at the same time, a high frequency interference voltage occurs in the line between C and D because the line supplied with the power I1 is severely interrupted by the power I2.
Furthermore, the second line capacity 17 is quickly charged with the power I2. If the voltage at the second line capacity 17 has reached the breakdown voltage ULI of the load 14 which is, for example, depicted as a Zener diode, the load 14 suddenly assumes the power I2, as shown in FIG. 8.
This again results in high frequency interferences because the metallic housing or the earth 19 is suddenly without power I2. At the same time a considerably high frequency interference voltage occurs in the line between C and D because the line is now also suddenly without power I2.
A further disadvantage is the fact that the potential at point B in reference to earth 19 jumps to a positive value corresponding to the load voltage ULI. On the other hand, because of the conductively controlled first switch 7 and the galvanic or high frequency grounding of the control system 2 via the capacitor 18, the potential at point A remains completely or nearly at earth potential. In case the circuit inductances 8, 9 values are equal, the potential at the consumer 10 in reference to earth jumps to half the value of the potential at point B. If the consumer 10 is not adequately insulated to ground 19, it can result in a breakdown or destruction of the consumer 10.